1. Field of the Invention
The present invention relates to a method for fabricating a semiconductor device. More particularly, the present invention relates to a method for fabricating an air gap between the interconnects using a hard mask.
2. Description of the Related Art
Advances in the semiconductor technology continuously decrease the semiconductor device dimension into the deep sub-micron territory. As the density of an integrated circuitry increases, the wafer surface becomes insufficient for the manufacturing of the necessary numbers of interconnects. To accommodate the increased number of interconnects, the multi-level metal conductive connect design becomes the approach for Very Large Scale Integration technology.
The continuous decrease in the distance between the metal conductive layers, however, is accompanied by an increase in the aspect ratio of the dielectric layer between the metal conductive layers. The coupling capacitance between the metal conductive layers is thereby increased, leading to the formation of a parasitic capacitance. Parasitic capacitance in a microelectronic device contributes to undesirable effects such as an increase of the RC delay time when electronic signals are
being transmitted between the metal linings. As a result, the speed of the electronic signal transmission between the metal linings is retarded and the operational speed of the semiconductor device is limited.
In order to reduce the transistor-capacitance delay time of the signal transmission, the development of a material with a low dielectric constant k has become the major trend in the semiconductor industry. Currently, materials with a low dielectric constant that are being developed mainly include the spin on polymer (SOP) and the organic spin on glass (OSOG), in which the dielectric constant is approximately between 2 and 4. As the manufacturing of semiconductors enters the deep sub-micron territory, the dielectric layer requires an even lower dielectric constant to accommodate the diminishment of the device dimensions and to improve the performance of the device. Air, having a dielectric constant of close to one and being inexpensive, has become one of the dielectric materials currently under development. If air can be used as a dielectric material, the insulation effect can be highly increased.